Magnetic transformer having increased bandwidth for high speed data communications

ABSTRACT

An isolation transformer includes a transformer core. First and second through-bores extend through the transformer core from a first surface to a second surface. Each through-bore has an elongated profile with at least a portion of the elongated profile providing a respective flat winding surface. The flat winding surfaces are spaced apart by a central portion of the transformer core. The transformer is wound with a six-wire cable having a central non-conductive core. First, second, third, fourth, fifth and sixth conductive wires are positioned around and adjacent to the central non-conductive core in a substantially equally spaced angular relationship. The second conductive wire is positioned between the first conductive wire and the third conductive wire; and the fifth conductive wire is positioned between the fourth conductive wire and the sixth conductive wire. The conductive wires are twisted about the central non-conductive core at a selected twist density.

RELATED APPLICATIONS

This application is a continuation application of U.S. patentapplication Ser. No. 15/725,047 filed on Oct. 4, 2017, which claimspriority under 35 USC 119(e) from U.S. Provisional Application No.62/480,757 filed on Apr. 3, 2017; and the contents both priorityapplications are incorporated by reference herein in their entireties.

BACKGROUND OF THE INVENTION Field of the Invention

This application is directed to conductors and circuit elements for usein high speed data communications, and, more particularly, toimprovements in baluns and twisted wire cables.

Description of the Related Art

Transformers are devices that transfer electrical energy from oneelectrical circuit to another electrical circuit through the use ofinductively coupled conductors. As is well understood, a varying currentin a primary winding creates a varying magnetic flux and thus a varyingmagnetic field through a secondary winding. This varying magnetic fieldinduces a varying electromotive force (“EMF”) or voltage in thesecondary winding. An ideal transformer assumes that all the magneticflux generated by the primary winding is coupled to every secondarywinding of the transformer. In practice however, some of the magneticflux generated by the primary winding exists outside the secondarywindings, thereby giving the appearance that the transformer has aninductance in series with the transformer windings. This non-idealoperating characteristic is known as leakage inductance.

Leakage inductance is caused by an imperfect coupling of the windings,which creates a leakage flux that does not link with all the turns ofthe secondary transformer windings. As a result, the voltage dropsacross the leakage reactance of the circuit resulting in a less thanideal voltage regulation, especially when the transformer is placedunder load. This is particularly problematic in high frequencyapplications where the high frequency of the electrical currentexacerbates the non-ideal parasitic effects seen in the transformer.

For years, engineers have recognized that reducing the amount of leakageinductance seen on a transformer increases the high frequencyperformance of the transformer. Heretofore, the most commonly usedmethods to reduce the amount of leakage inductance seen in a transformerhas traditionally been by twisting the primary and secondary wirestogether, interleaving the windings (e.g., interspersing individual orlayers of primary windings with secondary windings), or alternativelyimplementing a combination of both twisting and interleaving of thewindings in order to increase the coupling between windings. The purposeof both twisting and interleaving techniques is to attempt to distributeelectromagnetic energy (both internal energy and externally generatedenergy) to each of the primary and secondary windings as equally and ascompletely as possible. However, while it is possible to implement acombination of twisting and interleaving, twisting is often extremelydifficult to accomplish when interleaving more than one set of windings.This is primarily a result of the fact that once you have more than oneinterleaved winding, the order of the wires in the bundle needs to becarefully controlled in order to obtain the best coupling. This is oftendifficult to achieve when using both interleaving in combination withwire twisting.

For high frequency communications, small transformers with relativelyfew windings are used to electrically isolate network data lines fromlocal circuitry so that any potential differences to ground between thenetwork data lines and the local circuitry do not result in current flowbetween the data lines and the local circuitry. For example, FIG. 1illustrates a known transformer 100 that may be used for isolation. Suchan isolation transformer is often referred to as a “balun.” Asillustrated, the transformer includes a core 102 that comprises amagnetically permeable material having a relative magnetic permeability(μ/μ₀) of, for example, 1,500 to 5,000. A plurality of wires 104 arewound onto the core to form the windings of the transformer. In theillustrated embodiment, the wires are grouped in multi-wire (e.g.,three-wire) cables. For example, a first three-wire cable 106 mayinclude two primary wires and one secondary wire and a second three-wirecable 108 may include two additional primary wires another secondarywire. The three wires in each cable are twisted together to cause thethree wires in each cable to encounter similar perturbations causes byelectromagnetic noise.

The transformer core 102 is formed as an oval-shaped (e.g.,racetrack-shaped) body 110 with a first cylindrical through-bore 112spaced apart from a second cylindrical through-bore 114. An example ofsuch a transformer is described in detail in U.S. Pat. No. 7,924,130 for“Isolation Magnetic Devices Capable of Handling High-SpeedCommunications,” which is incorporated by reference herein in itsentirety. As described in U.S. Pat. No. 7,924,130, the completedtransformer is formed by threading the wires (cables) 104 through thefirst through-bore and through the second through-bore to form thewindings of the transformer. The ends of wires are selectivelyinterconnected to define the primary and secondary windings of thetransformer. One skilled in the art will appreciate that the circularthrough-bores that receive the wires cause the wires threaded throughthe through-bores to be spaced apart differently along thecircumferences of the through-bores. For example, the turns of the wirespositioned near the center of the core are closer together across thethickness of the core between the through-bores than the turns of thewires that are farther from the center of the core. As further shown inthe cross-sectional view of FIG. 2, the wires (cables) tend to bunch upwithin the through-bores rather than being evenly distributed within thethrough-bores. In some configurations, the bunching of the wires maycause the start of a particular winding to be positioned near the finishof the particular winding, which may increase the parasitic capacitancebetween the start and the finish of the winding.

SUMMARY OF THE INVENTION

Although the previously described cable and transformers are adequatefor high-speed data communications up to certain data transmission rates(e.g., up to 400 MHz frequency range), the need for higher datatransmission rates has resulted in a need for improvements in thecoupling between the primary and secondary windings of the transformer.

In view of the foregoing, a need exists for a system and method thatprovides enhanced coupling between the windings of an isolationtransformer in a high speed data communications coupler system.

One aspect of the embodiments disclosed herein is an isolationtransformer that includes a transformer core. First and secondthrough-bores extend through the transformer core from a first surfaceto a second surface. Each through-bore has an elongated profile with atleast a portion of the elongated profile providing a respective flatwinding surface. The flat winding surfaces are spaced apart by a centralportion of the transformer core. The transformer is wound with asix-wire cable having a central non-conductive core. First, second,third, fourth, fifth and sixth conductive wires are positioned aroundand adjacent to the central non-conductive core in a substantiallyequally spaced angular relationship. The second conductive wire ispositioned between the first conductive wire and the third conductivewire; and the fifth conductive wire is positioned between the fourthconductive wire and the sixth conductive wire. The conductive wires aretwisted about the central non-conductive core at a selected twistdensity.

Another aspect of the embodiments disclosed herein is an isolationtransformer comprising a transformer core having a first surface and asecond surface. A first through-bore extends through the transformercore from the first surface to the second surface. The firstthrough-bore has an elongated profile with at least a portion of theelongated profile providing a first flat winding surface. A secondthrough-bore extends through the transformer core from the first surfaceto the second surface. The second through-bore has an elongated profilewith at least a portion of the elongated profile providing a second flatwinding surface. The second flat winding surface is spaced apart fromthe first flat winding surface by a central portion of the transformercore. The transformer further includes at least one multi-wire cablecomprising a first conductive wire, a second conductive wire, a thirdconductive wire, a fourth conductive wire, a fifth conductive wire, anda sixth conductive wire. The second conductive wire is positionedbetween the first conductive wire and the third conductive wire. Thefifth conductive wire is positioned between the fourth conductive wireand the sixth conductive wire. In certain embodiments, each of the firstand second through-bores has an oval-shaped profile having a centralrectangular portion, a first semicircular end portion and a secondsemicircular end portion. Each of the first and second flat windingportions is defined by a respective side of the central rectangularportion of the respective through-bore. In certain embodiments, the atleast one multi-wire cable includes a first three-wire cable thatincludes the first conductive wire, the second conductive wire and thethird conductive wire, wherein the first, second and third conductivewires twisted together; and further includes a second three-wire cablethat includes the fourth conductive wire, the fifth conductive wire andthe sixth conductive wire, wherein the fourth, fifth and sixthconductive wires twisted together. In certain embodiments, the firstthree-wire cable and the second three-wire cable are wound onto thetransformer core with one turn of the first three-wire cable positionedbetween adjacent turns of the second three-wire core. In other certainembodiments, the at least one multi-wire cable comprises a six-wirecable that includes the first conductive wire, the second conductivewire, the third conductive wire, the fourth conductive wire, the fifthconductive wire and the sixth conductive wire, wherein the first,second, third, fourth, fifth and sixth conductive wires are helicallywound about a central non-conductive core.

Another aspect of the embodiments disclosed herein is a transformer corecomprising a magnetic material formed into a solid having at least afirst surface and a second surface. A first through-bore extends throughthe magnetic material from the first surface to the second surface. Thefirst through-bore has an elongated profile with at least a portion ofthe elongated profile providing a first flat winding surface. A secondthrough-bore extends through the magnetic material from the firstsurface to the second surface. The second through-bore has an elongatedprofile with at least a portion of the elongated profile providing asecond flat winding surface. The second flat winding surface is spacedapart from the first flat winding surface by a central portion of themagnetic material. In certain embodiments in accordance with thisaspect, each of the first and second through-bores has an oval-shapedprofile having a central rectangular portion, a first semicircular endportion and a second semicircular end portion. Each of the first andsecond flat winding portions is defined by a respective side of thecentral rectangular portion of the respective through-bore.

Another aspect of the embodiments disclosed herein is a multi-wire cablefor a transformer winding. The cable comprises a central non-conductivecore. At least a first conductive wire, a second conductive wire, athird conductive wire, a fourth conductive wire, a fifth conductivewire, and a sixth conductive wire are positioned around and adjacent tothe central non-conductive core in a substantially equally spacedangular relationship. The second conductive wire is positioned betweenthe first conductive wire and the third conductive wire. The fifthconductive wire is positioned between the fourth conductive wire and thesixth conductive wire. The conductive wires are twisted about thecentral non-conductive core at a selected twist density. In certainembodiments in accordance with this aspect, each conductive wire has acommon diameter corresponding to a selected wire gauge. The centralnon-conductive core has a diameter at least as great as the commondiameter of the conducive wires. In certain embodiments in accordancewith this aspect, the central non-conductive core comprises amonofilament material. In certain embodiments in accordance with thisaspect, the multi-wire cable comprises only six conductive wires and thecentral non-conductive wire. In certain embodiments in accordance withthis aspect, the multi-wire cable comprises eight conductive wires andthe central non-conductive wire. In certain embodiments in accordancewith this aspect, the multi-wire cable comprises nine conductive wiresand the central non-conductive wire.

Another aspect of the embodiments disclosed herein is high data ratecoupler system comprising an isolation transformer and a choke. Theisolation transformer includes a core having a first surface and asecond surface. A first through-bore extends through the transformercore from the first surface to the second surface. The firstthrough-bore has an elongated profile with at least a portion of theelongated profile providing a first flat winding surface. A secondthrough-bore extends through the transformer core from the first surfaceto the second surface. The second through-bore has an elongated profilewith at least a portion of the elongated profile providing a second flatwinding surface. The second flat winding surface is spaced apart fromthe first flat winding surface by a central portion of the transformercore. The transformer further includes at least one multi-wire cablecomprising a central non-conductive core, a first conductive wire, asecond conductive wire, a third conductive wire, a fourth conductivewire, a fifth conductive wire, and a sixth conductive wire. The secondconductive wire is positioned between the first conductive wire and thethird conductive wire. The fifth conductive wire is positioned betweenthe fourth conductive wire and the sixth conductive wire. The first andthird conductive wires form a first primary winding of the isolationtransformer; and the fourth and sixth conductive wires form a secondprimary winding of the isolation transformer. The first and secondprimary windings are connected in series to form a center-tapped primarywinding. The second wire forms a first secondary winding of theisolation transformer, and the fifth wire forms a second secondarywinding of the isolation transformer. The first and second secondarywindings are connected in series to form a center-tapped secondarywinding. The choke is wound with respective end segments of the secondconductive wire and the fifth conductive wire. In certain embodiments inaccordance with this aspect, the at least one multi-wire cable comprisessix conductive wires and a central non-conductive wire. In otherembodiments in accordance with this aspect, the at least one multi-wirecable comprises a first three-wire cable and a second three-wire cable.In certain embodiments having the first three-wire cable and the secondthree-wire cable, the first, second and third conductive wires are inthe first three-wire cable, and wherein the fourth, fifth and sixthconductive wires are in the second three-wire cable.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing aspects and other aspects of this disclosure are describedin detail below in connection with the accompanying drawing figures inwhich:

FIG. 1 illustrates a perspective view of a known isolation transformer;

FIG. 2 illustrates a cross-sectional view of the isolation transformerof FIG. 1 taken along the line 2-2 in FIG. 2;

FIG. 3 illustrates a perspective view of a transformer core havingelongated through-bores, the view showing the front, top and right sidesof the transformer core;

FIG. 4 illustrates a rotated perspective view of the transformer core ofFIG. 3, the view showing the rear, bottom and left sides of thetransformer core;

FIG. 5 illustrates a perspective view of a transformer incorporating thecore of FIGS. 3 and 4, the transformer including first and second coilscomprising three turns each of first and second three-wire cables;

FIG. 6 illustrates a cross-sectional view of the transformer of FIG. 5taken along the line 6-6 of FIG. 5;

FIG. 7 illustrates a schematic diagram of the transformer of FIGS. 5 and6;

FIG. 8 illustrates a segment of a six-wire cable having a centralnon-conductive core around which the six conductive wires are wound in atwisted pattern;

FIG. 9 illustrates a cross-sectional view of the six-wire cable of FIG.8 taken along the line 9-9 in FIG. 8;

FIG. 10 illustrates a perspective view of a transformer incorporatingthe transformer core of FIGS. 3 and 4 and the six-wire cable of FIGS. 8and 9;

FIG. 11 illustrates a cross-sectional view of the transformer of FIG. 10taken along the line 11-11 in FIG. 10;

FIG. 12 illustrates a schematic diagram of the transformer of FIGS. 10and 11 showing the six wires of the six-wire cable as windings about thecore of the transformer;

FIG. 13 illustrates a perspective view of a transformer in which thesix-wire cable of FIG. 8 is wound onto a toroidal core structure;

FIG. 14 illustrates a perspective view of a high data rate couplersystem that incorporates the transformer of FIGS. 10 and 11 with thesix-wire cable and a toroidal core wound with a three-wire cable;

FIG. 15 illustrates an enlarged perspective view of the transformer ofFIG. 14 showing the interconnections to the primary windings of thetransformer in more detail;

FIG. 16 illustrates an enlarged perspective view of the transformer ofFIG. 14 showing the interconnections to the secondary windings of thetransformer in more detail;

FIG. 17 illustrates a schematic diagram of the high data rate couplersystem of FIGS. 14-16 showing the interconnections of the primarywindings and the interconnections of the secondary windings and thetoroidal coil;

FIG. 18 illustrates a schematic diagram of a high data rate couplersystem similar to the system of FIG. 17 which incorporates thetransformer of FIGS. 5 and 6 in place of the transformer of FIGS. 10 and11;

FIG. 19 illustrates a perspective view of a high data rate couplersystem that incorporates the transformer of FIGS. 5 and 6 with the twothree-wire cables and a toroidal core wound with a three-wire cable;

FIG. 20 illustrates a cross-sectional view similar to the view of FIG. 8wherein the multi-wire cable comprises eight conductive wires around anon-conductive core; and

FIG. 21 illustrates a cross-sectional view similar to the view of FIG. 8wherein the multi-wire cable comprises nine conductive wires around anon-conductive core.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

An improved high data rate isolation transformer is disclosed in theattached drawings and is described below. The embodiment is disclosedfor illustration of the transformer and is not limiting except asdefined in the appended claims.

FIGS. 3 and 4 illustrate a transformer core 300 in accordance with adisclosed implementation. Unlike the core of the previously describedoval-shaped transformer 100 of FIGS. 1 and 2, the transformer core 300in FIGS. 3 and 4 has an overall box-like (parallelepiped) appearancehaving six generally rectangular sides. In the illustrated orientationreferenced to X, Y and Z coordinates, the core has a top surface 310, abottom surface 312, a left surface 314, a right surface 316, a frontsurface 318 and a rear surface 320. A first (top-bottom) central axis330 passes through the center of the core from the top surface to thebottom surface parallel to the Y axis. A second (left-right) centralaxis 332 passes through the center of the core from the left surface tothe right surface parallel to the X axis. A third (front-rear) centralaxis 334 passes through the center of the core from the front surface tothe rear surface parallel to the Z axis. The three central axesintersect at the center of the core. The references to top, bottom,left, right, front and rear are for convenience in providing thefollowing description. One skilled in the art will appreciate that thetransformer core can be oriented in a variety of different orientationsduring construction and in use.

In the illustrated embodiment, the transformer core 300 has a heightalong the top-bottom central axis 330 of approximately 0.136 inch, awidth along the left-right central axis 332 of approximately 0.120 inchand a thickness (depth) along the front-rear axis 334 of approximately0.120 inch. The dimensions are for example only and are not intended tobe limiting. As further shown in FIG. 3, the edges between the topsurface 310 and the bottom surface 312 and the adjacent left surface 314and right surface 316 may be filleted (e.g., rounded) to remove thesharp edges.

As further illustrated in FIGS. 3 and 4, the transformer core 300includes a first elongated through-bore 340 and a second elongatedthrough-bore 342. Each elongated through-bore extends through the corefrom the front surface 318 to the rear surface 320 in parallel with thefront-rear central axis 334. In the illustrated embodiment, the twoelongated through-bores are spaced substantially equally distant fromthe front-rear central axis and are also spaced equal distant from theleft-right central axis 332 of the core.

Unlike the previously described circular through-bores 110, 112 of thecore 100 of FIG. 1, the elongated through-bores 340, 342 of thetransformer core 300 of FIGS. 3 and 4 are generally oval-shaped (e.g.,racetrack-shaped). Each through-bore is wider in a left-to-rightdirection parallel to the left-right central axis 332 and is narrower ina top-to-bottom direction parallel to the top-bottom central axis 330.Each elongated through-bore has a generally rectangular central portion350. A first semicircular end portion 352 extends from the left end ofthe rectangular central portion. A second semicircular end portion 354extends from the right end of the rectangular central portion. Eachelongated through-bore has a respective inner flat surface 356 that isnearest to the center of the core and a respective outer flat surface358 that is farthest from the center of the core. A central portion 360of the core extends from the front surface 318 to the rear surface 320of the core between the two through-bores. The central portion of thecore has a nominal height between the respective flat surfaces of thetwo through-bores.

In the illustrated embodiment, each elongated through-bore 340, 342 hasan overall width (W) from the outer perimeter of the respective firstsemicircular end portion 352 to the outer perimeter of the secondsemicircular portion 354 of approximately 0.065 inch. In the illustratedembodiment, each elongated through-bore has a height (H) from therespective inner flat surface to the respective outer flat surface ofapproximately 0.034 inch, which corresponds to the diameter of eachsemicircular end portion. The rectangular central portion 350 of eachelongated through-bore has a width of approximately 0.31 inch. The innerflat surfaces of the through-bores are spaced apart from each other byapproximately 0.23 inch, which corresponds to the height of the centralportion 360 of the core. The foregoing dimensions and the spacing of theelongated through-bores are examples only and are not intended to belimiting.

FIG. 5 illustrates a perspective view of the transformer core 300 ofFIGS. 3 and 4 configured as part of a transformer 500 with a pluralityof turns of wires wound through the elongated through-bores 340, 342 andaround the central portion 360 of the core. FIG. 6 is a cross-sectionalview of the transformer of FIG. 5. In the illustrated embodiment, afirst three-wire cable 510 and a second three-wire cable 512 are woundaround the central portion of the core in an interleaved fashion suchthat three turns of the first cable are interleaved with three turns ofthe second cable. The resulting transformer is illustrated schematicallyin FIG. 7. For convenience in the following description, two of thewires in the first cable are labeled as N1 and N2, and the third wire inthe first cable is labeled as G. Two of the wires in the second cableare labeled in FIGS. 5-7 as B1 and B2, and the third wire in the secondcable is labeled as R. In FIGS. 5-7, the start of each wire (upper left)in FIG. 6 is further identified with an S suffix, and the finish of eachwire is labeled with an F suffix. The start of each wire is threadedfirst through the second (lower) elongated through-bore and out throughthe first (upper) through bore. The finish of each wire extends from thesecond (lower) elongated through-bore. The start and finishidentifications can be interchanged.

As illustrated schematically in FIG. 7, in a particular application ofthe transformer 500 of FIGS. 5 and 6, the starts (N1S and N2S) of the N1and N2 wires of the first cable 510 are connected together, and thefinishes (N1F and N2F) of the N1 and N2 wires are connected togethersuch that the N1 and N2 wires are connected in parallel for windingabout the central portion of the core. The starts (B1S and B2S) of theB1 and B2 wires in the second cable 512 are connected together, and thefinishes (B1F and B2F) of the B1 and B2 wires are connected togethersuch that the B1 and B2 wires are connected in parallel for windingabout the central portion of the core. The interconnected finishes (N1Fand N2F) of the N1 and N2 wires of the first cable are further connectedto the starts (B1S and B2S) of the B1 and B2 wires of the second cablesuch that the parallel connected N1 and N2 wires and the parallelconnected B1 and B2 wires are connected in series as a continuoussix-turn primary winding 700 of the transformer. The interconnectedfinishes N1F, N2F of the N1 and N2 wires and the starts B1S, B2S of theB1 and B2 wires form a center-tap 702 of the primary winding as shown inthe schematic diagram. The interconnected N1S and N2S end segments ofthe N1 and N2 wires form a first outer lead 704 of the primary winding.The interconnected B1F and B2F end segments of the B1 and B2 wires forma second outer lead 706 of the primary winding.

As further illustrated in FIG. 7, the finish (RF) of the R wire in thesecond cable 512 is connected to the start (GS) of the G wire in thefirst cable 510 such that the R wire and the G wire are connected inseries as a six-turn secondary winding. The common connection of thefinish (RF) of the R wire and the start (GS) of the G wire forms acenter-tap 712 of a secondary winding 710 of the transformer 500 asshown in the schematic diagram. The RS end segment of the R wire forms afirst outer lead 714 of the secondary winding. The GF end segment of theG wire forms a second outer lead 716 of the secondary winding. In theillustrated embodiment, the secondary windings are interconnected in across-coupled configuration as shown to further improve impedancematching in the passband by adding half of the interwinding capacitanceand reducing the leakage inductance.

As shown in a cross-sectional view in FIG. 6, the two cables 510, 512are positioned against the respective inner flat surfaces 356 (seeelement number 356 in FIGS. 3 and 4) of the elongated through-bores 340,342 such that each turn of each cable is positioned adjacent the centralportion 360 of the transformer core 300. If the sum of the diameters ofthe adjacent turns of the wire exceed the extent of the flat innersurfaces, the turns of the wires at one or both ends of the flat innersurfaces may extend into the semicircular end portions 352, 354 asshown; however, the small difference in the height of the centralportion of the core between the respective end turns relative to thenominal height of the central portion of the core between the flat innersurfaces of the elongated through-holes does not substantially affectthe desired uniformity of the coupling between the turns of the wires.

The structure of the transformer 500 of FIGS. 5-7 improves the operationof transformers at higher data communications rates by increasing thecoupling between the turns of the wires in the windings and alsoreducing the parasitic elements in the transformer that are parallelwith the winding (e.g., the distributed capacitance between the start ofthe winding and the finish of the winding, which are at opposite ends ofthe elongated bores as shown in FIG. 7.

The two interleaved three-wire cables 510, 512 of FIGS. 5-7 of thetransformer 500 provide coupling between the primary winding and thesecondary winding for data communications at wide bandwidths up toapproximately 1,800 MHz. However, winding the transformer with the twothree-wire cables requires that the two cables be wound onto thetransformer core 300 in two separate steps or by using a technique toallow the two cables to be wound at the same time while maintaining theperimeters of the two cables against the inner surfaces 356 of the core.

If the bandwidth provided by the two interleaved three-wire cables 510,512 is not required, the transformer core 300 can be wound with a singlemulti-wire cable. For example, FIG. 8 illustrates a segment of amulti-wire cable 800 that can be wound onto the transformer core in asingle operation. As illustrated, the multi-wire cable includes sixconductive magnet wires with a thin enameled insulator formed thereon.Such magnet wire is commercially available from many vendors. In theillustrated embodiment, the magnet wires comprise 38-gauge wires havingouter diameters of approximately 0.0045 inch; however, the followingdescription is readily adaptable to wires of a different gauge. Forconvenience in referring to the wires in the following discussion, thesix wires are labeled as B1, B2, R, N1, N2 and G. The selected labels B,R, N and G may refer to blue, red, natural and green colors,respectively; however, other colors or other techniques may also be usedto identify the wires. In a particular implementation, the six wires mayhave corresponding colors for the insulation to allow each particularwire to be easily identified when interconnected as described below.

As shown in FIG. 8, the six conductive magnet wires B1, B2, R, N1, N2, Gin the cable 800 are twisted around a central non-conductive corefilament 830 having a diameter generally corresponding to the diameterof each of the six magnet wires. For example, the core filament diametermay be the same as the diameter of the magnet wires, or the corefilament diameter may be slightly larger than the diameter of the magnetwire. Preferably, the core filament comprises a non-magnetic material.For example, in one embodiment, the non-conductive, non-magnetic corefilament comprises a monofilament material such as nylon, fluorocarbon,polyethylene, polyester, or other suitable material. Such materials maybe similar to materials used for fishing line. The six conductive wiresmay be twisted in a clockwise or counterclockwise direction around thecentral core filament. The clockwise twist direction is shown in FIG. 8.The twist density (or tightness) may be varied as required. In theillustrated embodiment, the twist density is selected to be in a rangeof 16 twists per inch (TPI) to 20 TPI. As illustrated, each of the sixconductive wires is helically wound about the central non-conductivecore filament with the start of the helical pattern of each conductivewire spaced apart angularly by 60 degrees with respect to the starts ofthe helical pattern of the two adjacent conductive wires. Accordingly,the centers of the six wires form a hexagonal pattern about the centralnon-conductive core filament as illustrated in the cross-sectional viewof the six-wire cable in FIG. 9.

In the illustrated embodiment of the six-wire cable 800, the R wire ispositioned between the B1 wire and the B2 wire, and the three wires forma first group of wires. The G wire is positioned between the N1 wire andthe N2 wire, and the three wires form a second group of wires. The B1wire is adjacent the N2 wire, and the B2 wire is adjacent to the N1wire. The numbering of the B wires and the numbering of the N wires isarbitrary in the embodiment described herein because each B wireperforms the same function and each N wire performs the same function aswill be apparent in the following description. The six conductive wiresare wound tightly around the central core 830. The inclusion of thecentral core prevents the six conductive wires from being forced inwardduring the twisting process. Thus, the six conductive wires retain theinitial B1-R-B2-N1-G-N2 configuration around the central core throughoutthe twisting process. The three wires in each group remain together overthe length of the cable with the R wire positioned tightly between theB1 and B2 wires and with the G wire positioned tightly between the N1and N2 wires. The six conductive wires also retain the desiredconfiguration when wound about the transformer core 300 as describedbelow.

The ease of winding the six-wire cable 800 is illustrated in FIGS. 10and 11 wherein the six-wire cable is wound onto the transformer core 300in the form of a three-turn coil 1010 threaded through the first (upper)elongated through-bore 340 and the second (lower) through-bore 342 toform a transformer 1000 structure around the central core portion 360 ofthe core. For the purposes of the following discussion, the three-turncoil “starts” as it enters the second (lower) elongated through bore and“finishes” as it exits the first (upper) elongated through-bore.Accordingly, a respective first end segment of each of the six wires N1,N2, B1, B2, G, R of the six-wire cable at the start end of the cable islabeled with a suffix “S” (e.g., N1S, N2S, B1S, B2S, GS, RS). Arespective second end segment of each of the six wires at the finish endof the cable is labeled with a suffix “F” (e.g., N1F, N2F, B1F, B2F, GF,RF).

The previously described transformer 500 required three turns each oftwo three-wire cables 510, 512 to be wound onto the transformer core,for a total of six winding turns. Unlike the transformer 500 of FIG. 5,the transformer 1000 of FIG. 10 only requires the single three-turnsingle coil 1010 to be wound onto the transformer core. As shown inFIGS. 10 and 11, the three turns of the six-wire cable 800 in the singlecoil occupy substantially less longitudinal (e.g., left-to-right) spacewithin the elongated through bores 340, 342 as compared to the six turnsof the two three-wire cables described above. Thus, each of the threeturns of the six-wire cable is positioned against the respective innerflat surfaces 356 of the through bores.

In addition to being easier to wind than the two three-wire cables 510,512, the single six-wire cable 800 may improve the balance or symmetrybetween the first and second groups of windings. As discussed above, thefirst group of windings comprises the B1 wire and the B2 wire along withthe R wire. The R wire is positioned tightly between the B1 wire and theB2 wire. The second group of windings comprises the N1 wire and the N2wire along with the G wire. The G wire is positioned tightly between theN1 wire and the N2 wire. The wiring positions of the two groups of wiresachieve symmetrical coupling between the two groups of wires (e.g., thecoupling from the B1 and B2 wires to the R wire is similar to thecoupling from the N1 and N2 wires to the G wire). A further advantage isthat the six wires of the six-wire cable twist in unison as the cable isthreaded through the elongated through bores and around the frontsurface 318 and rear surface 320 of the transformer core. Thus, the sixwires experience similar electromagnetic perturbations and otherperturbations.

The advantages of the single six-wire cable 800 over the two three-wirecables 510, 512 provided by the common helical winding about the centralnon-conductive core 810 are offset in part by a reduced bandwidth. Thefirst set of wires N1, G, N2 are closely wound with respect to thesecond set of wires B1, R, B2. The close winding increases parasiticcapacitive coupling between the two commonly wound sets of wires incomparison with the parasitic coupling between the two separately woundsets of wires in the two three-wire cables. The increased parasiticcapacitive coupling may reduce the overall bandwidth of the transformer1000 with respect to the transformer 500. For example, the transformer1000 wound with the six-wire cable may operate at a bandwidth up toapproximately 1,200 MHz in comparison to the approximately 1,800 MHzbandwidth of the transformer 500 wound with the two three-wire cables.

FIG. 12 illustrates a basic schematic diagram of the transformer 1000 ofFIGS. 10 and 11. As illustrated, the transformer comprises six windingswound onto the core 300. A first winding 1200 comprises the N1 wirebetween the start end segment N1S and the finish end segment N1F. Asecond winding 1210 comprises the N2 wire between the start end segmentN2S and the finish end segment N2F. A third winding 1220 comprises theB1 wire between the start end segment B1S and the finish end segmentB1F. A fourth winding 1230 comprises the B2 wire between the start endsegment B2S and the finish end segment B2F. A fifth winding 1240comprises the R wire between the start end segment RS and the finish endsegment RF. A sixth winding 1250 comprises the G wire between the startend segment GS and the finish end segment GF.

The six-wire cable 800 of FIG. 8 can also be used with other transformerconfigurations. For example, FIG. 13 illustrates a perspective view of atransformer 1300 in which the six-wire cable of FIG. 8 is wound onto atoroidal core structure 1310. The toroidal transformer configuration ofFIG. 13 includes the advantages of being able to wind all of thetransformer windings in a single operation, as described above withrespect to the transformer 1000 of FIGS. 10 and 11.

FIG. 14 illustrates an embodiment of a high data rate coupler system1400 that incorporates the transformer 1000 of FIGS. 10 and 11. Forexample, the high data rate coupler may operate at bandwidths up to1,200 MHz.

The coupler system 1400 of FIG. 14 includes the transformer 1000 woundwith the six-wire cable 800 of FIGS. 8 and 9, as described above. Thecoupler system further includes a toroidal choke 1410 comprising atoroidal core 1412 wound with a coil 1414 having a plurality of turns(e.g., three turns) of a three-wire cable. The toroidal choke isconnected to the transformer as described below. Extended ends of thesix-wire cable are selectively interconnected to interconnect thetransformer and the choke and to form leads to the transformer. Anenlarged view of a first set of interconnections is shown in FIG. 15. Anenlarged view of a second set of interconnections is shown in FIG. 16.When interconnected as shown in FIGS. 14-16, the transformer and thetoroidal choke form the electrical circuit illustrated schematically inFIG. 17.

In FIG. 15, the R wire and the G wire of the three-turn coil 1010 aretruncated at the first (upper) through-bore 340 and at the second(lower) through bore 342 of the core 300 so that only the connections tothe N1 wire, the N2 wire, the B1 wire and the B2 wire are shown. Asshown in FIG. 15 and as represented schematically in FIG. 17, therespective first end (start) segments N1S, N2S of the N1 wire and the N2wire extending from the second (lower) elongated through-bore of thecore 300 are twisted together to form a first two-wire cable 1420 with atwist density of between 16 and 20 twists per inch. The first two-wirecable formed by the first end segments N1S, N2S has a length extendingfrom the three-turn coil of approximately 1 inch. The exposed distalends (ends farthest from the three-turn coil) of the first end segmentsN1S, N2S are soldered or otherwise electrically connected together. Asshown schematically in FIG. 17, the first two-wire cable forms a firstouter lead 1432 of a primary winding 1430 of the center-tappedtransformer 1000.

As further shown in FIG. 15 and as shown schematically in FIG. 17, therespective second end segments N1F, N2F of the N1 wire and the N2 wireextending from the first (upper) elongated through-bore 340 of the core300 are twisted together with the respective first end segments B1S, B2Sof the B1 wire and the B2 wire extending from the second (lower)elongated through-bore 342. The four end segments N1F, N2F, B1S, B2Sform a four-wire cable 1440 that is twisted with a twist density ofbetween 16 and 20 TPI. The four end segments may have a length ofapproximately 1 inch. The exposed distal ends of the four end segmentsare soldered or otherwise electrically connected together. As shownschematically in FIG. 17, the four end segments form a center-tap lead1442 of the primary winding 1430 of the transformer 1000.

As further shown in FIG. 15 and as shown schematically in FIG. 17, therespective second end segments B1, B2F of the B1 wire and the B2 wireextending from the first (upper) elongated through-bore 340 of the core300 are twisted together to form a second two-wire cable 1450 with atwist density of between 16 and 20 twists per inch. The second two-wirecable formed by the second end segments B1F, B2F has a length extendingfrom the three-turn coil of approximately 1 inch. The exposed distalends of the second end segments B1F, B2F are soldered or otherwiseelectrically connected together. The second two-wire cable forms asecond outer lead 1452 of the primary winding 1440 of the center-tappedtransformer 1000.

In FIG. 16, the extended portions of the R wire and the G wire of thethree-turn coil 1010 are again shown. The extended portions of the N1wire, the N2 wire, the B1 wire and the B2 wire are truncated at thefirst (upper) through-bore 340 and at the second (lower) through bore342 of the core 300 so that the R wire and the G wire can be seen inFIG. 16. As shown in FIG. 16 and as represented schematically in FIG.17, the first end segment RS of the R wire extends from the second(lower) elongated through-bore 340 by a distance of approximately 0.15inch to approximately 0.2 inch. Similarly, the second end segment GF ofthe G wire extends from the first (upper) elongated through-bore 342 bya distance of approximately 0.1 inch to approximately 0.15 inch. Thedistal ends of the end segment RS and the end segment GF areelectrically connected to a first end of a third N wire. The third Nwire (without a suffix) is not part of the six-wire cable 800 of thetransformer 1000. As shown in FIG. 16, the two end segments RF, GS andthe end of the N wire form a center-tap 1462 of a secondary winding 1460of the transformer.

As further shown in FIG. 17, the first end segment RS of the R wireforms a first outer lead 1464 of the center-tapped secondary winding1460 of the transformer 1000. The second end segment GF of the G wireforms a second outer lead 1466 of the secondary winding. The first endsegment RS of the R wire and the second end segment GF of the G wire aretwisted together with the third N wire to form a three-wire cable 1470that extends from the transformer 1000 to the toroidal choke 1410, whichis spaced apart from the transformer by approximately 0.1 inch to 0.15inch. In the illustrated embodiment, the three-wire cable is twistedtogether with a twist density of approximately 10 twists per inch. Asillustrated in FIG. 14, the three-wire cable is wound around thetoroidal core 1412 of the toroidal choke to form the three-turn toroidalcoil 1414. The three turns of the coil are distributed evenly overapproximately 180 degrees of the circular core. As shown schematicallyin FIG. 17, the RS end segment of the R wire is wound into a first coil1472 to form a first winding of the toroidal choke and the GF endsegment of the G wire is wound into a second coil 1474 to form a secondwinding of the toroidal choke. The toroidal choke operates in aconventional manner to suppress common mode noise in the RS end segmentof the R wire and the GF end segment of the G wire when the two wiresform part of a data communications line. The N wire connected to thecenter-tap 1462 of the secondary winding 1460 of the transformer 1000also passes through toroidal core as a third coil 1476 wound with thefirst and second coils. The N wire is electrically connectable to asource (or a destination) for a DC voltage that provides power over anEthernet cable, as described, for example, in US Patent ApplicationPublication No. 2016/0187951 A1 to Buckmeier et al., which published onJun. 30, 2016, and which is incorporated by reference herein in itsentirety.

In alternative embodiments, the N wire may be extracted from thethree-wire cable 1470 prior to bypass the winding of the toroidal choke1410 such that the toroidal core is wound with only two wires, the RSend segment of the R wire and the GF end segment of the G wire. In afurther alternative configuration, if power over an Ethernet cable isnot required, the N wire from the center tap of the secondary winding ofthe transformer can be eliminated such that the toroidal core is woundwith only two wires, the RS end segment of the R wire and the GF endsegment of the G wire and is only connected to the isolation transformerby the two end segments.

As illustrated in FIGS. 14, 15 and 16, the extended end segments of thesix wires are continuous segments of the six-wire cable 800 forming thethree-turn coil 1010. The two outer leads 1432 and 1452 and thecenter-tap lead 1442 of the primary winding 1430 of the transformer 1000only require electrical connections to other circuitry (not shown) intowhich the coupler system 1400 is incorporated. Similarly, the R wire andthe G wire of the toroidal choke 1410 are uninterrupted continuations ofthe RS end segment of the R wire and the GF segment of G wire,respectively. The only electrical connection made within the immediatevicinity of the transformer is the electrical connection from the thirdN wire and the RF end segment of the R wire and the GS segment of the Gwire. By eliminating the electrical interconnections between the wireswithin the transformer and the toroidal choke, the transformer iscompact and simple to manufacture. Accordingly, the combination of thetransformer core 300, which has the elongated through-bores 340, 342,and the six-wire cable 800, which has all of the winding wires combinedinto a single compact cable provide substantial improvements inmanufacturability and functionality.

FIGS. 18 and 19 illustrate a coupler system 1800, which is similar tothe coupler system 1400 of FIGS. 14-17, and which operates at a higherdata rate. The coupler system of FIGS. 18 and 19 is implemented with thetransformer 500 of FIGS. 5 and 6, which incorporates the two three-wirecables 510, 512. As described above, the N1S and N2S end segments of thetwo cables are connected together to form the first outer lead 704 ofthe primary winding 700. The N1F, N2F, B1S and B2S end segments areconnected together to form the center-tap 702 of the primary winding.The B1F and B2F end segments are connected together to form the secondouter lead 706 of the primary winding. The RS end segment forms thefirst outer lead 714 of the secondary winding 710 of the transformer.The RF and GS end segments and an additional N wire form the center-tap712 of the secondary winding. The GF end segment forms the second outerlead 716 of the secondary winding. The toroidal coil 1410 is implementedas described above by twisting the first outer lead, the second outerlead and the additional N wire together and winding the three wires ontothe toroidal core 1412 to form the three coils of the toroidal choke.The coupler system of FIGS. 18 and 19 may operate at bandwidths of 1,800MHz in accordance with the requirements of the IEEE 802.3bq-2016 for a40 GBaseT interface.

The multi-wire cable of FIG. 8 can be configured to have additionalconductive wires around the non-conductive core. For example, FIG. 20illustrates a cable 1900 comprising eight conductive wires 1920helically around a non-conductive core 1910. In the illustratedembodiment wherein the conductive wires are 38-gauge wires (e.g.,approximately 0.0045 inch in diameter), the non-conductive core has adiameter of approximately 0.0073 inch, which is slightly larger than thediameter of a 34-gauge magnet wire. In FIG. 20, each helically woundwire is spaced apart angularly by 45 degrees from the two adjacentwires. As a further example, FIG. 21 illustrates a cross-sectional viewsimilar to the view of FIG. 8 wherein the multi-wire cable comprisesnine conductive wires 2020 around a non-conductive core 2010. In theillustrated embodiment wherein the conductive wires are 38-gauge wires(e.g., approximately 0.0045 inch in diameter), the non-conductive corehas a diameter of approximately 0.0087 inch, which is slightly largerthan the diameter of a 32-gauge magnet wire. In FIG. 21, each helicallywound wire is spaced apart angularly by 40 degrees from the two adjacentwires.

One skilled in art will appreciate that the foregoing embodiments areillustrative of the present invention. The present invention can beadvantageously incorporated into alternative embodiments while remainingwithin the spirit and scope of the present invention, as defined by theappended claims.

What is claimed is:
 1. An isolation transformer comprising: atransformer core having a first surface and a second surface; a firstthrough-bore extending through the transformer core from the firstsurface to the second surface, the first through-bore having anelongated profile with at least a portion of the elongated profileproviding a first flat winding surface; a second through-bore extendingthrough the transformer core from the first surface to the secondsurface, the second through-bore having an elongated profile with atleast a portion of the elongated profile providing a second flat windingsurface, the second flat winding surface spaced apart from the firstflat winding surface by a central portion of the transformer core; and amulti-wire cable comprising at least a first conductive wire, a secondconductive wire, a third conductive wire, a fourth conductive wire, afifth conductive wire, and a sixth conductive wire, the secondconductive wire positioned between the first conductive wire and thethird conductive wire and the fifth conductive wire positioned betweenthe fourth conductive wire and the sixth conductive wire, the first,second, third, fourth, fifth and sixth conductive wires helically woundabout a central non-conductive core, wherein the first and thirdconductive wires of the multi-wire cable form a first primary winding ofthe isolation transformer and the fourth and sixth conductive wires ofthe multi-wire cable form a second primary winding of the isolationtransformer, the first and second primary windings connected in seriesto form a center-tapped primary winding; and the second conductive wireof the multi-wire cable forms a first secondary winding of the isolationtransformer, and the fifth conductive wire of the multi-wire cable formsa second secondary winding of the isolation transformer, the first andsecond secondary windings connected in series to form a center-tappedsecondary winding.
 2. The isolation transformer as defined in claim 1,wherein each of the first and second through-bores has an oval-shapedprofile having a central rectangular portion, a first semicircular endportion and a second semicircular end portion, each of the first andsecond flat winding portions defined by a respective side of the centralrectangular portion of the respective through-bore.
 3. The isolationtransformer as defined in claim 1, wherein each conductive wire of themulti-wire cable has a common diameter corresponding to a selected wiregauge; and wherein the central non-conductive core has a diameter atleast as great as the common diameter of the conductive wires.
 4. Theisolation transformer as defined in claim 1, wherein the centralnon-conductive core of the multi-wire cable comprises a monofilamentmaterial.
 5. The isolation transformer as defined in claim 1, whereinthe multi-wire cable comprises only six conductive wires and the centralnon-conductive wire.
 6. The isolation transformer as defined in claim 1,wherein the multi-wire cable comprises eight conductive wires and thecentral non-conductive wire.
 7. The isolation transformer as defined inclaim 1, wherein the multi-wire cable comprises nine conductive wiresand the central non-conductive wire.
 8. The isolation transformer asdefined in claim 1, wherein the conductive wires are wound around thecentral non-conductive wire at a selected twist density.
 9. Theisolation transformer as defined in claim 1, further comprising a chokewound with respective end segments of the second conductive wire and thefifth conductive wire.